Polyolefin resins such as a polypropylene resin are widely used for manufacturing exterior and interior parts of automobiles, exterior parts of household electric apparatuses such as electric refrigerators and electric washing machines, and a variety of molded products such as trays, shelf boards and wrapping sheets.
The polyolefin resins are generally utilized in the form of polyolefin resin compositions containing fillers so as to improve such physical properties as rigidity and impact resistance. The fillers generally employed for these purposes are fibrous inorganic fillers or non-fibrous inorganic fillers.
Patent Publication 1 (JP 2009-167407A) discloses a polypropylene resin composition that can be molded with less mold-staining and less troubles so as to give a molded product showing high antistatic properties as well as high light-resistance with good moldability. The molded product shows good balance between rigidity and impact resistance, and has good appearance with less flow marks. The disclosed polypropylene resin composition comprises 99 to 60 weight parts of a polymer of polypropylene group, 1 to 40 weight parts of an inorganic filler (or inorganic filler material) having an average particle diameter of 0.01 to 100 μm, and 0.05 to 5 weight parts of a specific light stabilizer of the hindered amine type. In this publication, there are described non-fibrous inorganic fillers, fibrous inorganic fillers and their mixtures as inorganic fillers.
Patent Publication 2 (JP 2015-13978A) discloses a filler composition that can be incorporated into thermoplastic resins and thermosetting resins in which the filler composition comprises an inorganic fiber and spherical silica particles having a volume-average particle diameter of 0.01 to 5 μm. This publication has such description that resin compositions containing this filler composition shows good fluidity and further describes examples of the inorganic fibers such as carbonaceous fibers, fibers comprising carbonaceous materials as main components, glass and combinations of glass and other materials.
Patent Publication 3 (JP 2011-213514A) describes fine silica particles having surfaces treated with a silane-coupling agent and an organo-silazane and indicates that these fine silica particles show good affinity to resins and are kept from aggregation.
Recently, it is desired that automobiles have increased light-weight bodies for decreasing fuel consumption. For instance, exterior parts of automobiles such as bumpers are studied to reduce their thicknesses for decreasing their weights. However, the bumpers of automobiles are required, even in the case that their thicknesses are reduced, to still have high impact-resistance and high rigidity for keeping the bumpers from breakage when the bumpers are brought into contact with other automobiles or other solid materials, and further for keeping from deformation under pressures given by forces applied from the outside. However, since the molded product of the polypropylene resin that is widely used for manufacturing bumpers of automobiles shows a relationship of trade-off between its impact resistance and its rigidity. Therefore, it is known that if one of these properties increases, another property likely decreases.
The inventors of the present invention studied fillers described in each of the Patent Publications 1, 2 and 3 for the use as fillers for polyolefin resins.
As a result of the studies, the inventors have found that molded products having a thin thickness such as bumpers of automobiles manufactured using polyolefin resin containing fillers described in these patent publications hardly show such high impact resistance as required for the bumpers of automobiles, without decrease of rigidity.
Based on the above-described finding, the present inventors have studied to find a polyolefin resin composition such as a polypropylene resin composition that is employable for manufacturing a molded product showing both of high rigidity and high impact resistance.